This invention relates to reaming devices; and more particularly relates to a novel and improved method and apparatus for underreaming well bores and caverns and which is specifically adaptable for use in hard rock subsurface formations.
In conventional open hole completion, the well bore is drilled into the top portion of the productive formation and casing is run to the top of the productive formation and cemented in place. The well bore is then deepened through the productive formation and left open to communicate with the interior of the well bore. Generally, this method establishes more communication with the well bore than a conventional cased hole. The types of completion described are somewhat effective in formations with high permeability. However, with the recent increased number of well completions in formations having low permeability or low reservoir pressure, low production flow rates have resulted with long economic payout periods and unsatisfactory rates of return on investment. The reserves in place may be substantial, but the production flow rates are usually unsatisfactory. The conventional types of completion described provide insufficient productive formation surface area to communicate with the well bore. Further, there is insufficient well bore volume for efficient production or for the use of other downhole equipment; and do not increase well bore diameters enough to enable ease of intersection with other well bores.
I have previously devised reaming devices, such as, for example, that disclosed in U.S. Pat. No. 5,494,121 for CAVERN WELL COMPLETION METHOD AND APPARATUS. However, there is a previously unmet need for reaming tools which can be mounted at the lower end of a drill string for the purpose of carrying out high speed earth bore enlarging operations as well as for cavern well completions in hard rock formation with or without fluid assist and with or without rotatable cutter disks, stationary cutting teeth or other inserts.
It is therefore desirable to provide for a method and apparatus for substantially increasing the surface area of the production formation and volume area of the well bore in such a way as to result in substantially increased production rates and to overcome the numerous problems and drawbacks inherent in conventional open hole and cased hole completions as well as subsequent enhancement treatments. In particular, it is proposed to employ a novel and improved reaming device for enlarging a well bore diameter at the productive formation which is characterized by its ease of installation, operation, versatility and reliability in use.
It is an object of the present invention to provide for a novel and improved reaming tool for earth bore enlargement and cavern well completion operations which is highly versatile and efficient and durable in use.
Another object of the present invention is to provide for a novel and improved reaming tool adopted to be mounted on a conventional drill string and which employs a combination of cutter elements and jet discharge nozzles selectively positioned along the length of one or more cutter blades to achieve a uniform cutting force along the length of each blade.
A further object of the present invention is to provide for a novel and improved reaming tool which employs a unique combination of cutting inserts and fluid passages to carry out downhole cutting operations and specifically wherein the cutting elements may be employed alone or in combination with fluid pressure to perform different cutting and kerfing operations.
It is a still further object of the present invention to provide for a novel and improved reaming tool made up of pivotal cutter blades which employ a unique combination of cutter elements and fluid passages selectively oriented and spaced along the cutting edge of each blade to maximize cutting performance and speed.
In accordance with the present invention, a reaming tool has been devised for enlarging an earth bore in a subsurface formation wherein rotational drive means is lowered through the earth bore to a point at which it is desired to underream or enlarge the bore and wherein a plurality of elongated cutter blades are pivotally secured to a lower end of said drive means. Each of the cutter blades has a series of cutter disks mounted for rotation independently of the blades along a surface of the blade-engaging formation. Fluid delivery means communicates with a fluid circulation passage in each blade for delivery of fluid under pressure therethrough. A plurality of fluid discharge jets extend from said passage to expel fluid from said surface. The blades include radially inner and outer offset portions along a surface of each blade adapted to move into engagement with the formation, each of the offset portions including cutting members thereon.
In a preferred form, the cutter elements include a plurality of rotatable cutter disks which are disposed at radially spaced intervals along the length of each cutter blade, each disk oriented for rotation about an axis on the radius of curvature of the circular path of travel traced by each respective disk; and each cutting blade has offset cutting edges defined by radially spaced smaller cutter disks and larger cutter disks, respectively. In addition, an increased number of jet discharge nozzles is provided along the outer offset edge relative to those provided along the inner offset edge as a result of the greater area traversed by the outer edge. Still further, the nozzle locations are staggered with respect to the cutting element locations so that the cutting elements break up the material between the kerf lines formed by the nozzles. For example, if the nozzles are disposed only along one of the blades and the cutting elements disposed along the other of the blades, the cutting elements will break up that formation material between the kerf lines formed by the nozzles on the one cutting blade. If the cutting elements are positioned on both blades, they are preferably staggered with respect to one another so as to engage different radial distances in the formation between the kerf lines. Correspondingly, if the nozzles are positioned along both blades, they are offset with respect to one another to form kerf lines at different radial distances and thereby achieve enhanced cutting action. The number and spacing of cutting elements and nozzles along the offset edges will of course vary with the hardness of material being drilled, hole size and velocity of the fluid discharge.
The preferred method of reaming in a subsurface formation comprises the steps of lowering a plurality of cutter blades through the earth bore to a point at which it is desired to enlarge the bore, rotating the blades to cause them to swing outwardly into engagement with the wall of the bore, discharging a high velocity stream of fluid through a plurality of nozzles in at least one of the blades wherein a series of kerf lines are formed in concentric circles, placing a series of cutter elements on at least one other of the blades to break up the formation material between the kerf lines formed by the jet streams through the nozzles and orienting the elements to follow or track the kerf lines formed by the nozzles to assist in breaking up the rock or other material between the kerf lines.
There are additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. In this regard, the term xe2x80x9cdrill stringxe2x80x9d is employed herein to interchangeably refer to a string of drill pipe(s) or casing(s) or tubing(s). As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.